A manganese dioxide-silver nanostructure-based SERS nanoplatform for ultrasensitive tricyclazole detection in rice samples: effects of semiconductor morphology on charge transfer efficiency and SERS analytical performance

Taking advantage of metal-semiconductor junctions, functional nanocomposites have been designed and developed as active substrates for surface-enhanced Raman scattering (SERS) sensing systems. In this work, we prepared three types of nanocomposites based on manganese oxide (MnO 2 ) nanostructures and electrochemically synthesized silver nanoparticles (e-AgNPs), which differed according to the morphologies of MnO 2 . The SERS performance of MnO 2 nanosheet/e-Ag (MnO 2 -s/e-Ag), MnO 2 nanorod/e-Ag (MnO 2 -r/e-Ag), and MnO 2 nanowire/e-Ag (MnO 2 -w/e-Ag) was then evaluated using tricyclazole (TCZ), a commonly used pesticide, as an analyte. Compared to the others, MnO 2 -s/e-Ag exhibited the most remarkable SERS enhancement. Thanks to its large surface area and ability to accept/donate the electrons of the semiconductor, MnO 2 -s acted as a bridge to improve the charge transfer efficiency from e-Ag to TCZ. In addition, the MnO 2 content of the nanocomposites was also considered to optimize the SERS sensing performance. With the optimal MnO 2 content of 25 wt%, MnO 2 -s/e-Ag could achieve the best SERS performance, allowing the detection of TCZ at concentrations down to 6 × 10 −12 M in standard solutions and 10 −11 M in real rice samples. The role of MnO 2 in SERS enhancement of tricyclazole on MnO 2 /e-Ag was described in terms of charge transfer. The relationship between the morphology of MnO 2 nanostructures and the SERS sensing performance of nanocomposites was clarified.